1. Field of the Invention
The present invention relates to a grinding power tool and, in particular to a hand-guided electrical orbital sander, including a housing, a motor-driven grinding plate supported in the housing and having a plurality of suction openings, and a section channel provided in the housing for connecting the suction openings with a vacuum source.
2. Description of the Prior Air
Grinding power tools and, in particular, electrical grinding power tool with a suction device of the type described above are used when, e.g., unnecessary pollution of the environment and/or contamination of the user are to be avoided. Grinding dust, which is produced during grinding of, e.g., a constructional component, is removed from the constructional component with an air stream through a suction channel. To generate a necessary vacuum, an external vacuum source, in particular, a vacuum cleaner, is used. A further possibility of generating vacuum, consists in using of an internal vacuum source, e.g., a motor-driven ventilator, which is located in the tool housing. When an external vacuum source is used, it is often provided with a filter unit for filtering the grinding dust. When an internal vacuum source is provided in the power tool, the filter unit is provided in form of a filter bag which is releasably secured to the tool housing, in particular, to the suction channel.
An electrical grinding power tool of the type described above is disclosed, e.g., in German Publication DE-A1-195 30 542. The known power tool has a suction channel and, in particular, a suction union, which is provided at the suction channel, to which a filter bag is releasably secured. The suction union is provided at its free end with a valve that closes the suction union as soon as the suction process ends. The known power tool further includes a motor located in the tool housing for driving supported in the housing, grinding plate and ventilator. The ventilator is connected with the suction channel and provides for aspiration of the grinding dust-loaded air through the suction channel and for blowing the grinding dust-loaded air out of the suction channel and into the filter unit. The filter unit, the filter bag, is air-permeable but retains the grinding dust.
The known suction device provides for an adequate suction of the grinding duct without a need in an external vacuum source. Because the filter bag or the like is secured on the suction union, the filter bag can be secured on the suction union or replaced by the user himself.
A drawback of the known electrical grinding power tool consists in that the ventilator is driven by the tool motor and the size of the ventilator is limited by the size of the housing, which limits the suction capacity of the ventilator.
A further drawback consists in that only small filter units, in particular, filter bags may be used in order to insure compactness and, thereby, the handling of the power tool. Moreover, because the user has to often replace or clean the filter bag, loss of time takes place.
A similar grinding power tool is disclosed in U.S. Pat. No. 6,027,399. The grinding power tool of U.S. Pat. No. 6,027,399 is connected with an external dust suction means. In this grinding power tool, the motor-driven grinding plate has a plurality of opening which are closed with pegs. The grinding dust is aspirated directly from the grinding plate by an external vacuum source, e.g., vacuum cleaner, through suction holes provided in the bottom of the grinding plate.
The advantage of the grinding power tool disclosed in U.S. Pat. No. 6,027,399 consists in that the suction capacity can be adapted to the operational or work requirements by using a correspondingly dimensioned vacuum source. In addition, by providing closable openings, deposit of the dust on the constructional component is avoided.
A drawback of the grinding power tool of U.S. Pat. No. 6,027,399 consists in that dependent on the suction capacity of the used vacuum source, the opening in the grinding plate need be closed with pegs.
A further drawback of the grinding power tool of U.S. Pat. No. 6,027,399 consists in that the user should always carry a large number of closing pegs to be able to close the necessary openings. In addition, if no vacuum source is available at the operational site, the suction cannot take place.
Accordingly, an object of the present invention is to provide a compact and easily handled electrical grinding power tool with a suction capability.
A further object of the present invention is to provide an electrical grinding power tool with suction capability with which an adequate suction capacity is always available.
Another object of the present invention consists in providing an electrical grinding power tool with suction capability which can be economically produced.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a suction relief valve associated with the suction channel for controlling pressure in the suction channel.
The suction relief valve permits to limit the maximum vacuum in the suction channel. Thereby, no deposit of dust takes place on the treated constructional component even when a large capacity vacuum source is used. Further, by providing a suction relief valve at the suction channel, only a little pollution is observed as a result of displacement of the grinding plate, as. e.g., on the grinding plate itself. Thereby, a long service life of the electrical grinding power tool and, in particular, of the suction means is insured.
Advantageously, the suction relief valve is provided at the connection end region of the suction channel in order that a sufficient amount of air is available. In addition, the compactness and ease of handling of the power tool is not affected or affected only minimally. During the manufacturing of the electrical grinding power tool, the assembly of the suction relief valve can be effected without significant costs, which reduces the entire manufacturing costs.
Advantageously, the suction relief valve is arranged in a through-opening provided at the connection end region of the suction channel and has a resilient sealing member which sealingly closes the through-opening during idling of the power tool. Thereby, an easy and simple replacement of the suction relief valve is possible. When the difference between the environmental pressure and the pressure in the suction channel is large, the sealing member is pulled from its rest position, in which it closes through-opening, into the interior of the suction channel against its own biasing force. Thereby, at least partial equalization of pressures takes place.
The sealing member is advantageously secured on the suction channel with a clamp strap, which insures its easy mounting.
In order to insure a sufficiently high resiliency of the sealing member, it is made of a polymer material.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.